Blood Pressure. 2010; 19: 98–103
ORIGINAL ARTICLE
A comparison of blood pressure and pulse pressure values obtained by oscillometric and central measurements in hypertensive patients
MEHMET KAYRAK1, MEHMET S. ULGEN1, MEHMET YAZICI2, REMZI YILMAZ3, KENAN DEMIR1, YILDIZ DOGAN1, HAKAN OZHAN2, YUSUF ALIHANOGLU1, FATIH KOC1 & SAIT BODUR4 1Department
of Cardiology, Meram Medical Faculty, Selcuk University, Konya, Turkey, 2Department of Cardiology, Faculty of Medicine, Duzce University, Duzce, Turkey, 3Department of Cardiology, Faculty of Medicine, Harran University, SanliUrfa, Turkey, 4Department of Public Health, Meram Medical Faculty, Selcuk University, Konya, Turkey
Abstract Objective. Wide pulse pressure (PP) affects the accuracy of oscillometric blood pressure measurements (OBPM): however, the degree of this impact on different patient groups with wide PPs is unclear. This study will investigate the accuracy of OBPM in achieving target BP and PP in isolated systolic hypertension (ISH) group compared with mixed hypertension (MHT) group. Method. A total of 115 patients (70 with ISH and 45 with MHT) were enrolled in the study. Upper arm and wrist OBPM, obtained by OmronM3 and OmronR6 devices respectively, were compared with the simultaneously measured values from the ascending aorta. The ISH was defined as a systolic blood pressure (SBP) ⱖ140 mmHg and a diastolic blood pressure (DBP) ⬍90 mmHg. MHT was defined as a SBPⱖ140 mmHg and a DBPⱖ90 mmHg. Results. The mean central arterial blood pressure (BP) and central PP were higher in the ISH group than those in the MHT group. The upper arm OBPM underestimated the central SBP in two groups (⫺5 mmHg, ⫺3 mmHg, p⫽0.5, respectively), but overestimated DBP in the ISH group compared with MHT patients (6.8 mmHg, 1 mmHg, p⫽0.04, respectively). Wrist OBPM similarly underestimated to the central SBP in each group (⫺16 mmHg, ⫺19 mmHg, p⫽0.15), whereas the sum of overestimation of DBP was significantly higher in the ISH than in the MHT group (⫹6 mmHg, ⫺1 mmHg, p⫽0.001, respectively). Also, each of the devices underestimated the central PP in the ISH group (about 10 mmHg) as being higher than that of the MHT group. Conclusion. Oscillometric devices may be used for self-BP measurement in patients with ISH without clinically important disadvantages compared with the patients with MHT. For PP measurement in patients with ISH, there were substantial differences between intra-arterial and indirect arm BP measurements. Key Words: Blood pressure, central blood pressure, hypertension, isolated systolic hypertension, oscillometry, pulse pressure
Introduction Many oscillometric devices have been developed over the years, most of which are designed to reduce the influence of observer bias or to replace the observer with a means of detecting arterial wall movement by oscillometry. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) values obtained from oscillometric devices are derived using device-specific algorithms that are not disclosed by manufacturers (1). The oscillometric technique may be accurate when tested in a given clinical setting, but it has not been assessed throughout the wide pressure ranges that may occur in practice; as such, the possible effect
of altered vascular compliance on oscillometric blood pressure measurement (OBPM) is unclear in this population (2). Elderly subjects suffering from isolated systolic hypertension (ISH) commonly have increased pulse pressure (PP); wide PP, especially when it is greater than 55 mmHg, is an entity that affects the OBPM (3,4). The data based on these studies, however, were obtained from a population that consists of mixed hypertensive patients and a small percentage of the ISH group. In addition, the decreasing accuracy of OBPM was discussed by some authors (5), but these studies were frequently excluded in ISH patients. Despite the increasing number of
Correspondence: Yusuf Alihanoglu, Department of Cardiology, Meram Medical Faculty, Selcuk University, Akyokus/Meram PK 42090 Konya, Turkey. Tel: ⫹90 332 2236332. Fax: ⫹90 332 3237241. E-mail:
[email protected] (Received 7 October 2009; accepted 24 November 2009) ISSN 0803-7051 print/ISSN 1651-1999 online © 2010 Informa UK Ltd. (Informa Healthcare, Taylor & Francis AS) DOI: 10.3109/08037050903516318
Oscillometric vs central BP measurements in hypertensive patients
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validation studies, it is unclear as to which blood pressure (BP) category ISH patients or those with wide PP should be included in for the validation protocols. Wide PP was seen in patients with both ISH and mixed hypertension (MHT); the impact of hypertension types with wide PP on OBPM remains unclear in the current literature. The purpose of this study is to investigate the difference between OBPM and central arterial BP in those with ISH vs those with MHT. To do this, two different, previously validated types of oscillometric devices (6,7) were used to calculate the mean BP difference between central and OBPM in the ISH group, and the values were compared with those obtained from the MHT group.
pressure curve. Fractional PP, which is a marker of aortic pulsatility and elastic property, was presented as the ratio of PP to mean central arterial BP (8). The recording paper sweep speed was set to 25 mm/s during central BP measurements. An Omron R6 (with position sensor) was used for the wrist (Omron Medizintechnik, Mannheim, Germany) and an Omron M3 intellisense (HEM7051-E; Omron Healthcare Europe B.V., Hoofddorp, The Netherlands) was used for the upper arm. Each measurement was performed twice, and then compared with aortic BP values. The Omron M3 cuff was positioned in the mid-portion of the right upper arm, with the bladder directly over the brachial artery and the lower edge 2.5 cm above the antecubital space.
Materials and methods
Measurement protocol
Patient selection
The subjects were seated in a warm, quiet room and allowed to rest for at least 5 minbefore beginning the angiographic procedure. Demographic information such as age, height, weight and gender were recorded for each subject, as well as arm circumference, which was measured around the mid-point of the upper arm. Resting BP measurement was obtained with mercury sphygmomanometer before the angiography. According to the result of measurements with mercury sphygmomanometer, patients were divided into two groups (ISH and MHT). After patients’ data were collected, patients were transferred to the angiography room and the procedure was started. After the coronary angiographic procedure, initial readings were taken with the wrist and upper arm devices, and each measurement with these devices was performed twice. In accordance with the manufacturer’s instructions, care was taken to ensure that the patient’s wrist and upper arm regions were comfortably positioned at the level of the heart before the oscillometric devices were put in place.
In the study, 115 patients (70 of these with ISH and 45 age-matched patients with MHT) underwent a routine cardiac catheterization. Three centers were included in this study, the project was approved by the local ethics committee and informed consent was obtained for each patient. The most of the study investigators were blinded in accordance with the aim of the study. The investigators were randomly enrolled the patients with high BP who meet the inclusion criteria. At the end of the study, patients were divided into two groups and the data were analyzed. The aim of this study design is to decrease the observer bias, so the two groups were unbalanced. Exclusion criteria included abnormal atrial and ventricular rhythms, a high degree of atrioventricular (AV) blocks, hemodynamic instability, acute coronary syndrome, cardiogenic shock, severe valvular heart disease, end-stage renal failure, arm circumference greater than 38 cmor less than 20 cmand a body mass index (BMI) greater than 38 kg/m2 or less than 20 kg/m2. Patients receiving intravenously nitroglycerine or beta-blockers during the angiographic procedure were also excluded. BP measurement Intra-arterial BP measurements were performed with a 6F pigtail catheter positioned in the ascending aorta and attached to both a properly calibrated transducer and a monitoring system. The BP transducer was positioned at the same level as the BP cuff in order to avoid hydrostatic effects. A central measurement was performed simultaneously with each peripheral measurement. Recording of the central BP measurements began concurrently with deflation of the oscillometric device cuff. Means of 10–12 beats from the central aortic measurements were calculated as SBP and DBP. Mean central arterial BP was calculated by measuring the area under
Analysis and statistics The values are expressed as mean⫾standard deviation unless stated otherwise. Statistical analyses were performed by SPSS 13.0 packet program: the discrepancy between oscillometric and aortic BP measurements was tested using paired t-tests and the differences between the two groups were evaluated using Student’s t-tests for parametric variables and a χ2 test for categorical variables. A Pearson correlation test was used to determine linear associations among parametric variables. A two-tailed p-value of less than 0.05 was considered statistically significant.
Results The levels of central aortic SBP, antihypertensive medications and demographic features such as arm
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circumference, BMI and coronary artery disease frequency were similar in both groups. The patients’ characteristics were illustrated in Table I. The upper arm devices underestimated the central aortic SBP in each group whereas the wrist devices severely underestimated the central aortic SBP. However, the SBP difference between central aortic and OBPM was comparable in both groups (Figure 1a). The mean DBP difference between central aortic and OBPM was prominently higher in the ISH group than that of the MHT group for both types of the devices (Figure 1b). Thus, the difference between central and oscillometric measurements for both SBP and DBP values was prominent in the ISH group vs the MHT group. All SBP, DBP measurements and simultaneously measured aortic BP values were showed at the Table II. The PP obtained using the upper arm oscillometric devices was similar to the central PP in the MHT group (p⫽0.11): however, upper arm devices underestimated the PP by about 15 mmHg in the ISH group (Figure 1c). The wrist devices underestimated PP in both the ISH and the MHT group, but it was more prominent in former (Figure 1d). The effects of PP and aortic pulsatility on BP difference between central and oscillometric measurements were investigated in each group. The difference of DBP in the study group was correlated with PP and aortic pulsatility but the difference of SBP was not related to these parameters (Table II).
Discussion This is the first study investigating the difference between OBPM and central BP measurement in patients with the ISH group vs MHT. The study demonstrated that the sum of the underestimation of central SBP was similar in each group but DBP was more overestimated in the ISH group than that of MHT group. In addition, oscillometric devices more underestimated the central PP in the ISH group patients than the MHT group values. Although the values of mean SBP bias and DBP bias differ according to device, similar characteristic features in terms of overestimation and underestimation were demonstrated by the devices. The oscillometric technique is based on detecting the oscillations of the walls of the occluded artery. The oscillations of pressure in a sphygmomanometer cuff are recorded during gradual deflation, and the point of maximum oscillation corresponds to the mean intra-arterial pressure (9,10). SBP and DBP can only be estimated indirectly according to the some empirically derived algorithm. The mean difference between invasive measurements and the corresponding mean arterial pressure determined using the maximum-amplitude algorithm is, at most, 5 mmHg; however, it can reach approximately 40%
Table I. Demographic features, drugs and the results of the difference between oscillometric blood pressure (BP) measurement and central BP.
Age BMİ Arm circumference Diabetes mellitus, n (%) Smoking Female gender, n (%) CAD
ISH (n⫽70)
MHT (n⫽45)
p
58.6⫾6.6 30.6⫾5.6 29.0⫾3.6 25 (35.7) 22 (31.4) 30 (42.8) 36 (51.4)
57.9⫾8.6 29.8⫾4.7 28.8⫾3.3 14 (31.1) 11 (24.4) 20 (44.4) 22 (48.9)
0.66 0.50 0.73 0.20 0.22 0.41 0.46
28 (62) 32 (71) 24 (53) 1 (2) 7 (15)
0.62 0.32 0.45 0.17 0.19
Drugs, n (%) ACE-I/ARB, n (%) Diuretics, n (%) Ca antagonist, n (%) other No medications, n (%) Central SBP Central DBP Upper arm SBP Upper arm DBP Wrist SBP Wrist DBP Central PP Fractional PP Mean central arterial BP Mean SBP difference between upper arm-aorta Mean SBP difference between wrist-aorta Mean DBP difference between upper arm-aorta Mean DBP difference between wrist-aorta Mean PP difference between upper arm-aorta Mean PP difference between wrist-aorta Mercury sphygmomanometer SBP Mercury sphygmomanometer SBP
39 42 31 4 10
(55) (60) (44) (5) (14)
178.6⫾12.5 77.2⫾7.6 168.3⫾18.4 83.4⫾9.4 159.2⫾18.5 83.2⫾10.5 101.3⫾13.7 0.91⫾0.12 110.9⫾7.0 ⫺5.0⫾15.7
179.4⫾14.0 95.5⫾5.4 174.0⫾14.1 95.8⫾11.5 163.8⫾25.4 94.4⫾11.5 83.6⫾16.3 0.67⫾0.13 123.4⫾10.5 ⫺3.0⫾16.1
0.78 0.001 0.17 0.001 0.29 0.001 0.001 0.001 0.001 0.58
⫺19.0⫾14.1
⫺15.5⫾13.9
0.15
6.8⫾10.2
1.0⫾11.3
0.04
6.0⫾10.6
⫺1.1⫾11.0
0.001
12.8⫾11.5
3.5⫾12.8
0.001
25.2⫾14.4
14.2⫾14.1
0.001
167.0⫾16.2
170.4⫾20.0
0.31
83.5⫾8.5
92.4⫾9.6
0.001
ISH, isolated systolic hypertension; MHT, mixed hypertension; BMI, body mass index; CAD, coronary artery disease; ACE-I, angiotensin-converting enzyme inhibitor; ARB, angiotensin receptor blocker; SBP, systolic blood pressure; DBP, diastolic blood pressure; PP, pulse pressure.
of the invasive measurement in individual cases (11). It is known that the measurement of BP using a maximum-amplitude algorithm depends on several of variables besides mean BP, such as arterial mechanical properties, the pulse shape of the BP, PP, arm tissue and cuff mechanical properties, the cuff volume, and heart rate (3). In a recent study, Westhoff investigated the impact of PP on the accuracy of wrist OBPM (12).
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Figure 1. (a) A comparison of the systolic blood pressure (SBP) difference between central and oscillometric blood pressure (BP) measurements; (b) the mean diastolic blood pressure (DBP) difference between central and oscillometric BP measurements in patients with isolated systolic hypertension (ISH) compared with the mixed hypertension (MHT) group; (c) pulse pressure difference between aortic and upper arm oscillometric measurements in patients with ISH and MHT; (d) pulse pressure difference between aortic and wrist oscillometric measurements in patients with ISH and MHT.
In all, 33 patients, 10 patients of which had ISH and 85% of which had high PP (⬎50 mmHg), were enrolled in the study. They found that mean systolic bias was 10.2 mmHg and mean diastolic bias was 4.8 mmHg. In addition, it was demonstrated that the systolic bias significantly depended on PP, whereas the diastolic bias was independent of PP. However, the impact of the measurements for the patients with ISH on the study results remains unclear. Although the age-related rise in SBP was linear in patients aged 30–40 years, and was slightly steeper for women than for men, DBP falls progressively beginning at age 50 (13). If SBP was solely monitored in people aged 50–59 years, it could falsely categorize up to 10% of the hypertensive population (14). Systolic HT is more common than diastolic HT, and SBP contributes to more of the global disease burden attributable to HT than DBP does (15). However, strong proof from the Framingham studies suggests that, in elderly people, PP measurement is more accurate than either SBP or DBP in assessing cardiovascular risk. For this reason, correct measurement of PP, as well as BP, is essential (16). Therefore, based on the current results, increased underestimation of PP in the ISH group compared with the
MHT group may be accepted as a major limitation of oscillometric devices. The elderly constitute a significant portion of the hypertensive patient population, and these patients differ from other patient groups in certain characteristics such as increased aortic stiffness, decreased pulse wave amplification and wide PP. The prevalence of ISH is quite high in these patients (17). Altunkan & Altunkan studied the validation of the wrist oscillometric device in 76 elderly patients; the results indicated that the mean difference for the mercury sphygmomanometer was –0.3⫾6.5 mmHg for SBP, and 2.8⫾4.8 mmHg for DBP in the study group. On the other hand, although the number of patients with ISH was particularly high in this group, those patients were excluded from the study (18). Pannarale et al. pointed out that it might be difficult for the present algorithm of the devices to calculate SBP and DBP away from the measured mean BP in patients with wide PP (19); according to current knowledge, there is no data available regarding the use of oscillometric devices in patients with ISH. The authors of this report believe that a solution to this problem depends on certain characteristic ratios. It was emphasized above that SBP and DBP are calculated according to an empirically derived
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Table II. Correlation between central blood pressure (BP) devices and BP difference between central and oscillometric measurements. Group and BP differences ISH Mean SBP difference between upper arm-aorta Mean SBP difference between wrist-aorta Mean DBP difference between upper arm-aorta Mean DBP difference between wrist-aorta MHT Mean SBP difference between upper arm-aorta Mean SBP difference between wrist-aorta Mean DBP difference between upper arm-aorta Mean DBP difference between wrist-aorta
Mean central arterial BP (r)
PP (r)
Fractional PP (r)
available commercial instruments, these algorithms are typically proprietary, vary according to individual manufacturers and sometimes vary according to individual devices (21). The proprietary information includes whether manufacturers use fixed or variable characteristic ratios, and, if the latter are used, what rules determine how those ratios vary. On the basis of the present study, the authors advise that characteristic diastolic ratios should be reassessed by manufacturers for patients with ISH. It is reasonable that the type of HT may be automatically detected by oscillometric devices via calculated BP and PP values, and that these devices may recalculate BP with the appropriate characteristic ratios defining for ISH patients.
⫺0.174
⫺0.188
⫺0.044
⫺0.217
0.113
0.182
⫺0.389∗∗
0.310∗
0.424∗∗
⫺0.235∗
0.287∗
0.381∗∗
⫺0.468∗∗
⫺0.448∗∗
⫺0.400∗
⫺0.245
⫺0.256
⫺0.210
Limitations
⫺0.231
⫺0.161
⫺0.096
0.184
0.317∗
First, this study does not evaluate the validation of the devices: typically, assessment of validation oscillometric devices is performed using mercury sphygmomanometers. Second, only two types of device and totally six devices were used in the study. The authors accept that these devices are prototypes in their groups and that the main technique of the oscillometric devices is similar. Third, although the incidence of ISH is higher in the elderly population, the mean ages of the groups in this study were relatively young. Fourth, because of a diminished compressibility of the artery by the cuff, a falsely high BP reading – which is termed pseudohypertension in elderly patients – may sometimes be recorded by the BP measurement devices. However, these patients represent a small percentage of elderly patients, and studies that have been performed using healthy elderly subjects have not shown a great discrepancy between direct and indirect measurements of BP compared with younger subjects. Therefore, this may be accepted as a minor limitation of the study. Another important limitation of this study includes obtaining patients’ BP measurements while they are in the supine position, which is the recommended position for BP measurements. Admittedly, this subject remains under discussion. In addition, a large standard cuff (22⫻35 cm) for the upper arm device was used in our study because it is the only type of cuff that is commonly used for BP measurements in routine clinical practice; in addition some devices were manufactured with only one cuff size. We realize that the use of an inappropriate cuff could lead to systematic underestimation or overestimation of BP when the ratio of bladder width to arm circumference differs from 0.40 (22). For this reason, the patients with arm circumferences greater than 38 cmor a BMI greater than 38 kg/m2 or less than 20 kg/m2 were excluded from the study. In this study, both arm circumference and BMI were similar and in acceptable limits in two groups that were studied. Finally, the
0.419∗∗
∗Correlation
is significant at the 0.05 level (two-tailed). is significant at the 0.01 level (two-tailed). r ⫽correlation coefficient obtained by Spearrman’s correlation analysis. ISH, isolated systolic hypertension; SBP, systolic blood pressure; DBP, diastolic blood pressure; MHT, mixed hypertension. ∗∗Correlation
algorithm. The algorithm of each device analysis demonstrates various features of the oscillometric waveform, including the systolic and diastolic characteristic ratios (14). Systolic characteristic ratio can be calculated by oscillometric pulse amplitude when the cuff pressure equals to the value of systolic pressure divided by peak oscillometric pulse amplitude. Similarly, diastolic characteristic ratio can be calculated by oscillometric pulse amplitude when the cuff pressure equals to the value of diastolic pressure divided by peak oscillometric pulse amplitude (20). Although the general principle was defined by systolic and diastolic characteristic ratios, the device specific characteristic ratio was not known for any of the oscillometric devices. In addition, the systolic and diastolic characteristic ratios differ between patients (14). A systolic range between 0.45 and 0.57 and a diastolic range between 0.69 and 0.89 were defined for patients by Geddes et al. in an experimental study (20). Studies using mathematical models demonstrate that these ratios are affected by arterial wall visco-elastic properties as well as arterial pressure pulse amplitudes. The models also reveal similar results to those of Geddes et al.; typical systolic and diastolic characteristic ratios varied from 0.46 to 0.64 and from 0.59 to 0.80 respectively (20). The characteristic ratios used by different manufacturers are unknown for both normotensive and hypertensive patients. In currently
Oscillometric vs central BP measurements in hypertensive patients effects of anti hypertensive drugs on central and oscillometric BP difference were remained unclear. The most of the patients was taking combined drug therapy and the study sample was not large enough to determine the effects of the drugs. However, drug therapies were comparable between two groups. It needs additional investigation in this area.
Conclusion Despite the limitations of this study, oscillometric devices, especially upper arm devices, demonstrated sufficient characteristics for the measurement of SBP in patients with ISH and MHT. However, the oscillometric method may have some limitations in measuring central DBP and PP in patients with ISH. This limitation may be clinically insignificant regarding the management of patients with ISH compared with MHT; nevertheless, it is essential that unsatisfactory characteristics of these devices should be addressed by device manufacturers ,since for patients with wide pressure ranges, it is necessary to define BP ranges, PP ranges, characteristic diastolic ratios and the validation criteria. Finally, additional controlled studies on this subject should be performed in the future.
Acknowledgment All devices using for the study were taken from Turkey distributors of Omron Healthcare Co., Ltd. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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